Kinetics of ATP and inorganic phosphate release during hydrolysis of ATP by rabbit skeletal actomyosin subfragment 1: Oxygen exchange between water and ATP or phosphate

We have used the technique of phosphate:water oxygen exchange to measure the rate of ATP and P_i release and P_i binding to myosin subfragment 1 and actomyosin subfragment 1 from rabbit skeletal muscle. The oxygen exchange distributions for ATP and P_i release fit a simple kinetic model with a single set of rate constants for each step. For actomyosin subfragment 1 (20°C, pH 7.0, I = 50 mM), the rate constant governing ATP release is ∼8 s^-1, P_i release is at ∼60 s^-1 and P_i rebinds to an ADP state at >120 M^-1 s^-1. These rate constants are similar to those that may occur for undistorted cross-bridges within glycerinated rabbit psoas fibers (Bowater, R., Webb, M. R., and Ferenczi, M. A. (1989) J. Biol. Chem. 264, 7193-7201.